1. Field of the Invention
The invention relates to a sheet feeding apparatus for separating and feeding sheets such as stacked originals and recording mediums one by one, and an image forming apparatus provided with the sheet feeding apparatus.
2. Description of Related Art
There are known an image forming apparatus of the ink jet type for discharging ink to a recording medium such as recording paper to thereby form an image thereon, and an image forming apparatus of the electrophotographic type for forming an image on a recording medium by the use of a developer (toner), and these image forming apparatuses are provided with a sheet feeding apparatus for supplying the recording medium to an image forming portion.
Now, in some printers, as a sheet feeding apparatus for supplying a recording medium (hereinafter referred to as the sheet) to image forming means, provision is made of a multisheet feeding apparatus of a construction in which sheets set on a tray by a user are fed out, besides a sheet feeding apparatus of a construction in which sheets are fed out from a sheet feeding cassette containing the sheets therein. The multisheet feeding apparatus can set and feed sheets of various sizes and sheets of various kinds, and is efficient for the feeding of a small quantity of sheets, and the feeding of spatial paper such as thick paper or film paper.
An example of the conventional multisheet feeding apparatus will hereinafter be described with reference to FIGS. 6 to 8 of the accompanying drawings. FIG. 6 is a longitudinal cross-sectional view of the multisheet feeding apparatus, FIG. 7 is a perspective view of a separating pad, and FIG. 8 is an enlarged view showing a state in which a sheet is being separated by a sheet feeding roller and the separating pad.
The multisheet feeding apparatus 50 is provided with an intermediate plate 54 on which a plurality of sheets P are stacked, a side regulating plate 82 for regulating the widthwise position of the sheets P stacked on the intermediate plate 54, and an intermediate plate spring 56 for upwardly biasing the leading edge side end portion of the intermediate plate 54 in the sheet feeding direction. Above the intermediate plate spring 56, there is disposed a sheet feeding roller 58 for contacting with the sheets P stacked on the intermediate plate 54 to thereby feed out the sheets P one by one in the sheet feeding direction (the direction indicated by the arrow C).
Downstream of the sheet feeding roller 58 in the sheet feeding direction, there is disposed a sheet feeding guide 60 for guiding the sheet P fed out by the sheet feeding roller 58 to a pair of registration rollers 38 disposed on the downstream side in the sheet feeding direction. A pair of U-shaped grooves 62 (shown in FIG. 8) are formed at the right and left of the sheet feeding guide 60 as viewed in a direction orthogonal to the sheet feeding direction on the upstream side in the sheet feeding direction, and the opening 62a of each groove 62 faces downwardly.
A separating pad 70 is disposed adjacent to and upstream of the sheet feeding guide 60 in the sheet feeding direction. The separating pad 70 is comprised of a plate-shaped separating pad holder 70a provided with two pivot shafts 72 orthogonal to the sheet feeding direction on the downstream side in the sheet feeding direction, and a rectangular separating pad member 74 stuck on the upstream side surface of the separating pad holder 70a in the sheet feeding direction and formed of urethane rubber containing cork or the like. The two pivot shafts 72 of the separating pad holder 70a fit into the grooves 62, whereby the separating pad 70 is supported for pivotal movement.
Below the separating pad holder 70a, there is disposed a separating spring 76 comprising a coil spring for upwardly biasing the separating pad holder 70a. Since the separating spring 76 pushes up that portion of the separating pad holder 70a which is opposite to the pivot shaft 72 from below it, the separating pad holder 70a is pivotally moved about the pivot shaft 72. As the result, the separating pad member 74 is urged against the sheet feeding roller 58. Accordingly, the sheet feeding roller 58 is rotated in the direction indicated by the arrow D, whereby the stacked sheet is fed out from the intermediate plate 54, and when two or more sheets are fed out, they are separated one by one between the separating pad member 74 and the sheet feeding roller 58.
Now, to feed the sheet P smoothly in the sheet feeding direction, it is necessary that the surface of the separating pad member 74 be urged against the outer peripheral surface of the sheet feeding roller 58 with uniform contact pressure, and if the contact pressure is non-uniform, the sheet P may not be fed smoothly. When for example, greater contact pressure acts on one of the portions of the separating pad member 74 in the left to right direction thereof (the direction orthogonal to the direction indicated by the arrow C) than on the other portion, the sheet P being separated may be skew-fed or the sheet P may not be separated but may be jammed near the separating pad member 74.
In order that as described above, the surface of the separating pad member 74 may be urged against the outer peripheral surface of the sheet feeding roller 58 with uniform contact pressure, it is necessary that the line of contact 74a (shown in FIG. 7) when the separating pad member 74 contacts with the sheet feeding roller 58 and the center line of pivotal movement 72a (shown in FIG. 7) of the pivot shafts 72 of the separating pad holder 70a be parallel to each other. However, the accuracy of the position at which the sheet feeding guide 60 is fixed to the main body of the printer 10 or the accuracy of the shape thereof is sometimes bad due to the deformation or the like of the separating pad holder 70a and therefore, the line of contact 74a and the center line of pivotal movement 72a sometimes do not become parallel to each other.
Accordingly, when the pivot shafts 72 are fitted into the grooves 62 without any gap to such a degree that the pivot shafts 72 can freely pivotally move in the grooves 62, it is difficult due to the above-mentioned accuracy for the line of contact 74a and the center line of pivotal movement 72a to become parallel to each other. So, the grooves 62 are formed relatively larger than the outer diameter of the pivot shafts 72 so that irrespective of the above-mentioned accuracy, the line of contact 74a and the center line of pivotal movement 72a may become parallel to each other. By so constructing, the surface of the separating pad member 74 is urged against the outer peripheral surface of the sheet feeding roller 58 with uniform contact pressure.
Now, the coefficient of friction of the sheet feeding roller 58 and the coefficient of friction of the separating pad member 74 with respect to the sheet P differ from each other. Also, as described above, the grooves 62 are larger than the outer diameter of the pivot shafts 72 and therefore, there is more or less play or slop between these two. Therefore, when the sheet P nipped by and between the separating pad member 74 and the sheet feeding roller 58 is fed, the sheet P and the separating pad member 74 may rub against each other to thereby cause stick-slip motion. Due to the stick-slip motion, there occurs vibration and occurs an abnormal sound called pad chatter (squeak).
So, as techniques for preventing the pad chatter, the following techniques (1) to (4) are under consideration:
(1) The technique of disposing a member for contacting with the front side or the backside of the sheet P on the downstream side of the position, in which the sheet feeding roller 58 and the separating pad member 74 nip the sheet P therebetween, in the sheet feeding direction, and stopping the vibration of the sheet P;
(2) The technique of weakening the force with which the separating pad member 74 urges the sheet feeding roller 58 and preventing the stick-slip motion to thereby prevent the pad chatter;
(3) The technique of contriving the weight and shape of the separating pad holder 70a to change the resonance point of the separating pad holder 70a and decrease the vibration of the separating pad holder 70a; and
(4) The technique of fitting the pivot shafts 72 into the grooves 62 without any gap to thereby prevent the vibration of the separating pad holder 70a. 
However, according to the technique (1), the vibration of the sheet P can be stopped, but the vibration of the separating pad holder 70a cannot be stopped and therefore, the pad chatter cannot be completely prevented.
According to the technique (2), the possibility of the separation of the sheet P becoming incomplete is great and therefore, the sheets P may be double-fed, and the sheet feeding performance is reduced.
According to the technique (3), the vibration of the separating pad holder 70a can be mitigated, but depending on the thickness, density and stiffness of the sheet P, the pad chatter occurs and cannot be sufficiently coped with.
According to the technique (4), the contact pressure with which the separating pad member 74 contacts with the sheet feeding roller 58 becomes non-uniform, and the sheet P is not fed smoothly and skew feed or jam or the like is liable to occur and the sheet feeding performance may be reduced.
In view of the above-noted circumstances, the present invention has as its object to provide a sheet feeding apparatus in which pad chatter is prevented without the sheet feeding performance being reduced.
The sheet feeding apparatus of the prevent invention for achieving the above object is a sheet feeding apparatus provided with a sheet feeding rotary member rotatable in a direction for feeding sheets, and a separating pad biased toward the sheet feeding rotary member, and for separating the sheets one by one between the sheet feeding rotary member and the separating pad and feeding the sheets, wherein a vibration absorbing member for absorbing the vibration of the separating pad is interposed between the separating pad and a pad supporting portion for pivotally supporting the separating pad.
Also, the sheet feeding apparatus of the present invention is provided with a sheet feeding rotary member rotatable in a direction for feeding sheets, and a separating pad biased toward the sheet feeding rotary member, and for separating the sheets one by one between the sheet feeding rotary member and the separating pad and feeding the sheets, wherein the space between the separating pad and a pad supporting portion for pivotally supporting the separating pad is filled with an elastic adhesive.